1. Field of the Invention
The present invention generally relates to radar systems and, more particularly, to a radar apparatus and method suitable for detecting small, slow moving targets in the presence of high background clutter.
2. Description of the Related Art
In the past, radar systems have been used to detect and track relatively large, fast moving targets by the military and others. These targets have been typically artillery projectiles, rockets, people, automobiles, aircraft, etc. Detecting very small, slow moving targets at short distances, in the presence of high background clutter, has not been a high priority.
There have been a number of attempts to design a radar system to detect small, slow moving targets. These radar systems have not been very successful for a number of reasons. First, using a pulse radar to detect and track small, slow moving targets has been plagued with difficulties. The radar cross section of the target is very small, and any background clutter tends to blind the radar. The pulse radar has a minimum range, primarily determined by the transmitter pulse width. A typical minimum range of this type of radar is of the order of many hundreds of feet. At this range, identifying small targets is virtually impossible. Tracking a swarm of flying insects is nearly impossible due to the very small radar cross section. The target is not homogenous, and a good radar lock on a small undulating mass is very difficult.
Secondly, several attempts have been made to use a Continuous Wave (CW) Doppler Radar to detect small slowly moving targets. A doppler radar is sensitive to velocity, and a slow moving target generates a doppler frequency of the order of a few cycles per second. Insects normally move slowly over a few tens of millimeters during a measurement period. For reliable detection the target must generate a number of Doppler cycles by moving in a straight line towards or away from the radar antenna. An insect moving many wavelengths in a straight line in such a direction is unlikely.
Therefore, there is a need in the art for a radar apparatus and method that can detect small, slow moving targets in the presence of high background clutter.
The disadvantages associated with the prior art are overcome by a radar apparatus and method for detecting small, slow moving targets wherein the radar return signals from background objects as well as the target are viewed by the radar as a composite single signature return. The apparatus comprises a balanced bridge structure that can achieve a null balance even though the background clutter consists of many components at varying distances from the radar. The target sensitivity of the radar depends upon how deep a null of the clutter signal the radar can achieve. A very small change in the target position changes the composite clutter signature and causes the null to shift. The change in the null is then more easily detected.